1. Field of the Invention
The present invention relates to a method and apparatus for reducing the electrical power consumed by motor-driven appliances. More specifically, the present invention relates to a method and apparatus for optimizing the power factor of a.c. induction motor-driven appliances and reducing the inrush current associated with their operation. More specifically still, the present invention relates to a method and apparatus that optimizes the power factor of plug-in motor-driven appliances such as refrigerators, freezers, window air conditioners, clothes washing machines, or clothes dryers and hard-wired motor-driven appliances such as furnace blowers, central air conditioners, well-water pumps, and the like, while simultaneously reducing the inrush current of such motor-driven appliances.
2. Background of the Invention
In industrialized nations, motor-driven appliances typically found in residential units are ubiquitous and are also found in churches, schools, restaurants, and a myriad of small businesses. Many millions of such motor-driven appliances have been mass produced and collectively consume megawatts of electrical power annually. In contrast, the tools, equipment, and systems typically found in various industries are highly specialized and collectively they consume significantly less electrical power annually than motor-driven appliances.
Typically, motor-driven appliances are ultimately connected to a power transformer via conductors that may be several hundred feet in length. Another several tens of feet of conductors may extend from a circuit breaker panel to such motor-driven appliances within residential units, churches, schools, and small business buildings. Thus, several hundred feet of conductors may intervene between motor-driven appliances and the power transformers supplying electric power to them. The direct current, hereafter “DC”, resistance of said conductors dissipates the alternating current, hereafter “AC”, electrical current flowing to the house as Real Power which is the basis of residential monthly utility company charges. Since Real Power varies as the square of the magnitude of electrical current, reducing the magnitude of the average electrical current flowing through said conductors significantly reduces that house's monthly utility bill.
Specifically, most houses contain several ⅛th to 8 horsepower AC induction motor-driven appliances that perform a variety of essential functions for its occupants. The AC induction motors of such motor-driven appliances are of the following types:                1. Split-Phase Motors.        2. Capacitor Split-Phase Motors.        3. Permanent Split-Phase Motors.        
Such motors are relatively inexpensive, simple to construct, reliable, and have a reasonably long operating life. Furthermore, they are sufficiently powerful to perform a wide variety of utilitarian tasks, e.g. driving compressors for the refrigeration of foods, circulating the air, and so on.
However, such motors are relatively inefficient with respect to their ability to convert electrical power into mechanical power. Such motors are characterized as inductive loads which cause the voltage at the motor terminals to be substantially out-of-phase with the current flowing through the motors. Consequently, such motors operate inefficiently and draw more electrical current from the local utility company than is necessary resulting in unnecessarily large monthly utility bills. Furthermore, collectively, such motors in the households of the world's industrialized nations waste megawatts of electrical power annually.
The energy efficiency of such motors may be optimized by connecting a suitable capacitance in parallel with such motors to form a resonant circuit in which motor voltage and current are aligned while simultaneously drawing a minimum of current from the utility company. That is, such motors may be power factor corrected where power factor is defined as the ratio of the real power consumed by such motors divided by the apparent power. PF is a real number between 0.0 and 1.00 while the power factor of such motors is typically ranges between 0.45 and 0.70. By convention, optimal power factor correction of such motors is considered to be a power factor greater than, or equal to, 0.95.
The energy efficiency of such motors can be further improved by limiting their inrush current. Each and every time such motors are switched on, they draw 6 to 10 times their rated Full Load Ampere (FLA) current for about one second which is called inrush current. A typical household motor-driven appliance may turn on, and off, more than 1440 times per month drawing 6 to 10 times their rated FLA for more than 20 minutes. Collectively, the five or six typical household motor-driven appliances could draw 6 to 10 their FLA for about 100 to 120 minutes each month. As stated above, the real power dissipated in the conductors that connect motor-driven appliances to a distant power transformer increases as the square of the current magnitude. Thus, limiting inrush current will significantly reduce the average energy consumption of residential units en masse while reducing energy costs, i.e. utility bills.
3. PRIOR ART
Prior art inventions relied upon a preliminary, trial and error, multi-step power factor sizing procedure to determine a residential unit's overall power factor. More specifically, the first step in the prior art sizing procedure necessitated switching the motor-driven appliances of the residential unit under test into a particular on/off configuration assumed to be either a “worst case” scenario or a “typical” scenario. For example, a worst case scenario is usually considered to be one in which all household motor-driven appliances are switched on. For another example, a typical scenario may be one in which the refrigerator and central air conditioner are switched on while all other motor-driven appliances are switched off.
In the second prior art step, a switched capacitor bank box is connected in parallel with the residential unit's 208-230 VAC power mains and a suitable digital multi-meter is connected thereto to measure the residential unit's power factor. In the third prior art step, the switches of the switched capacitor bank box are toggled to switch various combinations of capacitors in, and out, of parallel electrical connection with the residential unit's power mains and reading the resulting power factor on the digital multi-meter. By trial and error, the switched capacitor bank box switches are toggled until the power factor is optimized, i.e. equal to, or greater than, 0.95. In the next prior art step, the capacitance that power factor optimized the overall residential unit is recorded. The next prior art step consists of manufacturing a custom power factor correcting device for that particular residential unit. The final step in the prior art is actually installing the power factor correcting device on, or in, the residential unit under test.
However, as can be seen, the prior art suffers from many drawbacks. First, it is predicated upon an assumed and unrealistic on/off configuration of a residential unit's motor-driven appliances. That is, the power factor of residential units as seen from their power mains changes over a wide range of values as various motor-driven appliances are automatically and/or manually turned on and off over time. Consequently, is that the capacitance of the installed power factor correction device seldom, if ever, optimizes the residential unit's power factor. Thus, the energy conserving and energy cost saving capabilities of the prior art are inherently and severely limited.
A second prior art drawback is its trial and error, convoluted, and time-consuming, sizing procedure that necessitates travel to each residential unit where the prior art is to be deployed. It is estimated that the U.S. is host to some 178 million households. Clearly, travel to each and every one of these 178 million households and executing the sizing procedure of the prior art is impractical. Consequently, the commercial success of the prior art has been inherently and severely limited. A third prior art drawback is its requirement that a licensed electrician must install each and every one of its instances as they are connected to the power mains of residential units. A fourth prior art drawback is its dependence upon a limited number of special, expensive, awkward to operate, switched capacitor bank boxes.
Clearly, there is a need for a residential unit power factor correction invention that maintains the residential unit's power factor at optimal levels regardless of the on/off configuration of its motor-driven appliances resulting in maximum energy conservation and energy cost savings possible. Clearly, there is a need for a residential unit power factor correction invention that can be mass produced and practically sold to the global market without execution of the sizing procedure of the prior art.